1. Field of the Invention
The present invention relates to a sheath composition containing a polyolefine resin and flame-retardant particles mixed therein, as well as a cable using the sheath composition.
2. Description of the Related Art
Halogen based flame-retardant agents containing halogen atom have conventionally been added to sheath compositions for cables to add flame resistance thereto. Although halogen based flame-retardant agents exhibit superior flame retardancy, they may generate harmful halogenated dioxins when burned. Therefore, various flame-retardant agents for replacing the halogen based flame-retardant agents have been studied.
Typical examples of flame-retardant agents that replace the halogen based flame-retardant agents are metal hydroxides (metal hydrates) such as magnesium hydroxide, as described in Japanese Patent Application Laid-Open (JP-A) Nos. 2001-302851, 2004-168878 and 2003-34793. However, when cables using sheath compositions containing magnesium hydroxide are left in a highly humid atmosphere, magnesium carbonate may deposit on the surfaces of the cables through a reaction between the magnesium hydroxide and carbon dioxide in the air. This deposition of magnesium carbonate is known as a whitening phenomenon, and may lead to deterioration of flexibility, windability and flame resistance of cables.
Further, since flame retardancy of the metal hydrates is lower than that of the halogen based flame-retardant agents, and the like, it is necessary to blend a large amount of metal hydrate in a resin to obtain necessary flame resistance of the resin. However, if a large amount of metal hydrate is blended in a resin, problems arise such as deterioration of dynamic performances of the resin and lowering of moldability of the resin.